Because of their hands-free convenience and ability to include more than one conversationalist at either end of a telephone call, speakerphones are currently in widespread use today, both for business and personal communications. Indeed, many low-cost telephone sets sold today have some speakerphone capability built into them. The speaker is often located under the handset, which is not an ideal location for the speaker, but is used to conserve space, and virtually all speakerphones sold today employ a loudspeaker that radiates, or “fires,” generally upward and/or forward from the upper or forward-facing surface of the phone. Business conferencing speakerphones are a typical manifestation of a speakerphone in which the speaker points upward, and the one or more microphones of the phone are typically distributed around the periphery of the phone and as far away from the speaker output as is practically possible to minimize the amount of “acoustic echo” manifested by the phone during operation.
All telephone sets can manifest two kinds of echoes, viz., an “acoustic echo” from feedback in the acoustic path between the earphone or speaker of the phone and its microphone, and a “line echo” that originates in the switched network that routes a call between stations. Acoustic echo is typically not a substantial problem in a wired telephone with a handset. However, acoustic feedback is a much greater problem in speakerphones, because both the room in which the phone is located and the contents thereof become part of the audio system and acoustic path from the speaker to the microphone. Accordingly, speakerphones typically incorporate some electronic circuitry adapted either to suppress, cancel, or filter out unwanted acoustic echo during operation. Examples of such echo suppression or cancellation circuitry can be found in, e.g., U.S. Pat. No. 6,711,259 to R. Haimi-Cohen al. and U.S. Pat. No. 6,904,146 to S. Dormer et al., respectively. It would be advantageous if the complexity, and hence, cost, of such circuitry could be substantially reduced, if not completely eliminated.
Additionally, it is desirable to achieve better low-frequency sound definition and high-frequency sound dispersion by the loudspeaker of the phone in order to increase speech intelligibility in teleconferences. This is particularly the case in “wideband” telephone transmissions (i.e., in a frequency band of about between about 150 Hz to about 7200 Hz) to enable users to better discern the vocal characteristics of far-end talkers, and thereby enable them to be easily identified in those instances in which there are many persons engaged in a conference call.
Accordingly, there is a long-felt but as yet unsatisfied need in the field for a speakerphone design that inherently reduces the amount of acoustic echo present in the phone, thereby resulting in the need for less complex, and hence, less costly echo cancellation circuitry, and one that also provides better low-frequency sound definition and high-frequency sound dispersion by the loudspeaker of the phone.